The brevetoxins are neurotoxins produced by the dinofiagellate, Karenia brevis, which can cause serious illness in humans. People are exposed to brevetoxins through seafood consumption, dermal contact in water or breathing seaspray aerosols. The effects of these harmful toxins and how natural antagonists protect in their presence will be investigated to understand the nature of toxicity in fish and mammals. Since prior studies show that brevetoxins bind to orphan receptors on site 5 of voltage sensitive sodium channels, competition between toxin and potential antagonists will be examined. From receptor binding experiments in rat brain synaptosomes, the equilibrium disassociation constant, inhibition constant, and binding maximum of new compounds will be determined. Due to the recent increase and severity of toxic blooms worldwide, this project with its chemical and molecular approach to understanding toxic blooms, will have broad human and environmental impacts. Among the impacts this project will have on human health, results could guide the synthesis of possible therapeutics for human illness caused by toxins.